Between 2000 and 2013, the Earth was hit by 26 asteroids that exploded with a force of between one and 600 kilotons – an average of one every six months. Even more concerning is that in all cases the asteroids themselves weren't detected in space and only came to light when they detonated in Earth's atmosphere.

The study was carried out by the B612 Foundation, a group set up by three former astronauts who are worried about the threat of asteroids to life on Earth. The foundation's CEO (and former shuttle pilot) Dr. Ed Lu presented the report's findings at a press conference in Seattle's Museum of Flight on Tuesday.

"While most large asteroids with the potential to destroy an entire country or continent have been detected, less than 10,000 of the more than a million dangerous asteroids with the potential to destroy an entire major metropolitan area have been found by all existing space or terrestrially operated observatories," said Luhttp://www.theregister.co.uk/2014/04/22/...ix_months/